You can basically replace 'incel' with 'scruffy virgins'. That's all they are. Of course, some of them will be toxic and blame their issues on others but there is no 'incel movement'. It is not an ideology. Subculture is the right term, I think. Birds of a feather, and all that.
In the case of the shooter, perhaps being immersed in an online society where the suggestion of being weird, unlikable, and out of place is so easily accepted and reinforced may have contributed to eventually being pushed to a mental break point, but he surely didn't kill in the name of virgins everywhere.
I think things like this:
A SOUTHEND councillor says a so-called "incel" movement is a threat to women - following urgent warnings from a former chief prosecutor.
www.echo-news.co.uk
To track the ‘incel’ diatribes uttered and read by Jake Davison, murdering women can seem like the logical conclusion to their seething hatred
www.theguardian.com
only serve to further ostracise other scruffy virgins. Tell someone they're the bogeyman enough times, and eventually they'll act like one. But most of them are just sad, depressed and lonely. They won't go on killing sprees, but they might kill themselves.
The direction some in the media are taking this story isn't good for anyone.